OMAPDSS: move blocking mgr enable/disable to compat layer

dispc_mgr_enable_sync and dispc_mgr_disable_sync are only used with the
compat mode. Non-compat will use the simpler enable and disable
functions.

This patch moves the synchronous enable/disable code to the compat
layer. A new file is created, dispc-compat.c, which contains low level
dispc compat code (versus apply.c, which contains slightly higher level
compat code).

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>